Tech Front: Advanced Electrochemical Machining

Tech Front is edited by Senior Editor Jim Lorincz

The smallest precision parts and dies with intricate features and details can be machined with high-quality surface finishes in production volumes with an advanced electrochemical machining (ECM) process called Precision Electrolytic Machining (PEM) from PEM Technologies (Natrona Heights, PA). Conductive metals including tempered steel, stainless, Hastelloy, Nitinol, aluminum, and exotic alloys can be completely machined, including roughing and finishing, as well as deburring, in a single operation with high repeatability.

The PEM process electrolytically machines away metal from parts without creating mechanical or thermal stress, undesirable surface conditions, or machining marks. The PEM process removes metal with a tool that never touches the part in a method that removes metal atom by atom in a process that is just the opposite of electroplating. The process is especially effective for machining features that are difficult or impossible to create by conventional methods achieving machining accuracies of 5–25 µm.

The PEM process incorporates a pulsed DC power source and an oscillating cathode tool for roughing, finishing, and polishing intricate features, including cavities, contours, and odd angles and shapes in small precision parts. In the PEM process, a cathode (tool) is advanced into an anode (workpiece). The metal removal current is pulsed while in close proximity (typically 10—20 µm gap), and then retracted. As electrons cross the gap during the pulse, material on the workpiece is dissolved, as the tool forms the desired shape. Pressurized electrolyte is injected at a set temperature while the gap between tool and workpiece is open to flush away the metal hydroxide formed in the process.

Typically, a full form electrode Z-axis movement is in the 1–1.5 mm/min range. The volumetric machining rate depends on the configuration of the tool electrode. The PEM process has the capability of machining with multiple identical tool electrodes simultaneously, multiplying the average per-part machining rate by the number of parts being machined per cycle for low-to-high production runs. The process has a theoretical maximum material removal rate of a tenth of a cubic inch per minute.

Feature size is geometry-dependent and is sometimes governed by the ability to fabricate micro electrodes. For example, grooves a few microns deep by tens of microns wide are possible. Features that are 100 µm or more in one direction and millimeters in another are typical. However, both material and geometry play a major role in determining what the process is capable of producing. Typical tolerance for this process is in the 10–14 µm range, which implies the limits of feature size capability.

The PEM processing system is modular comprising a processing machine (PEMMachine), a power module (PEMPower) providing direct current that is synchronized with the oscillating head of the machine, an automated electrolyte system (PEMAqua) to micro-filter and control pH of the electrolyte, and a PC-based control to monitor and control the process. Plant cooling water or chiller is required for the process.

The Case for S-Pads

Hardinge Inc. (Elmira, NY) lays out the case for S-pad tooling for multispindle automatics, CNC lathes, and VMCs. S-pads can be shared between many brands of machines whether the master collet is mounted directly in a machine spindle (single or multiple), in a collet adaptation chuck, or in a collet block. The style-S master collet was originally designed for multispindle automatic screw machines. Operators in multispindle shops know how much faster it is to change pads, rather than collets, from job-to-job.

The same benefits can be offered to operators of CNC lathes and VMCs as well. Collet pads can be changed more quickly than a standard collet, the cost is lower, and the pads require much less storage space. Twelve sets of S-pads take up less space in a tool drawer, cost less, and change over faster than 12 solid collets.

Hardinge points out that its standard S-pads are hardened and ground for long life. Semi-hard and soft emergency pads can be bored-to-size on the machine for the best possible concentricity. Hardinge has a dedicated S-pad manufacturing cell enabling the company to maintain stock availability on more than 1000 sizes of S-pads in a variety of styles. Patented style-S pads can be changed without removing the master collet from the spindle, thus reducing changeover time. For example, on an eight-spindle automatic, all the pads can be changed in 15–30 min as compared to 2–3 hr that it would take to change the solid collets.

Hardinge S-pads feature dovetail anchor design to securely hold the pad in place so it can’t be dislodged under normal use. The design eliminates any pressure on the clamp. There are no holes in the OD of the master collet, or on the ID of the pads, resulting in maximum bearing on the workpiece and the spindle collet seat.

Hardinge S-pads are available in S10 through S50 sizes to fit style-S master collets used in screw machines and CNC lathes. Style-S master collets designed for Hardinge collet-ready CNC lathes are available in 16C, 20C, 25C, B42, and B65. HCAC collet adaptation chucks are available for chuck-style lathes to accept style-S master collet and pads. S-pads can also be used in the Hardinge FlexC collet blocks, as well as 16C collet blocks, for three and four-axis milling applications. Pads are available in round, hexagon, and square with smooth or serrated order holes and special shapes.

For more information on Hardinge master collets and pads, go to www.shophardinge.com, or telephone 800-843-8801.

CNC Upgrades LegacyRotary Transfer Machines

Two add-on CNC systems from Hydromat (St. Louis) are successfully upgrading hydraulically driven legacy rotary transfer machines with the company’s cost-effective EPIC CNC technology. The two systems, the EPIC RS (Remote System) and EPIC SS (System Six), feature a full CNC drive system that provides a simple plug-and-play control architecture for each tool spindle. The CNC technology was introduced on the EPIC R/T machines that Hydromat introduced in 2003. The two systems are designed to simplify CNC hardware components in order to reduce the overall cost of adding EPIC CNC technology to existing Hydromat machines.

The EPIC RS system consists of a control unit for a single EPIC tool spindle and a compact tablet computer used for programming, offering users the advantage of EPIC EMC (Embedded Motion Control) technology that previously couldn’t be added to legacy Hydromat machines. A tablet computer is plugged into the RS to download the cutting program. The tablet can then be moved to another EPIC unit or carried away for programming work to be done off-line, away from the shop floor. The legacy Hydromat’s control stays intact and works as before. The EPIC RS tablet computer holds all the programs and is easily moved from unit to unit as needed. The EPIC RS is well-suited for adding one to three EPIC units on one machine, or a number of units on several machines.

The new EPIC SS (System Six) connects up to six EPIC CNC tool-spindle units on one legacy Hydromat machine. It comes equipped with the full-size EPIC operator interface on a stand-alone floor mounted pedestal. The original control and the new EPIC SS control work together to give users a fast upgrade to multiunit, multiaxis EPIC CNC Hydromat capabilities. The plug-and-play control system is added to a machine and the legacy Hydromat’s control stays intact and works as before. Legacy Hydromat users can use EPIC tool spindle units they may have in stock or can purchase new units.

For more information on Hydromat Inc., go towww.hydromat.com, or telephone 314-432-4644.

This article was first published in the February 2012 edition of Manufacturing Engineering magazine. Click here for PDF.